The present invention refers to a particular kind of arrangement for positioning a sensor in a removable manner in close vicinity of or in contact with a critical point or a critical zone of a cylindrical body, typically although not solely of metal, and in particular near an end portion of the body.
In an ideal manner, the above cited arrangement can be used in accommodating a removable thermocouple device for measuring the temperature of a nozzle for the injection of a flow of molten thermoplastic resin and, as a result, for indirectly measuring the temperature of the molten resin. For this reason, reference will be specifically made in the following description to such an application, although it shall be appreciated that the present invention may be used as well in all technical contexts and applications in which the need arises or is felt for the outside temperature of a cylindrical body to be measured, in accordance with the appended claims.
More specifically, the above cited nozzle is preferably used in machines for infection moulding thermoplastic resin, when a flow of such a resin in its molten, i.e. fluid state, flowing in either from appropriate conduits blown as “hot runners” in the art, and situated inside a related platen, or directly from the injector of the moulding machine, is injected towards and into a plurality of injection-moulding cavities defined by pairs of respective half-moulds.
The term “hot runner” is a term that is commonly used in the typical technical parlance in this particular field, so that the use thereof in this context will not give rise to any difficulty for those skilled in the art.
It is a widely used practice to make use of thermocouple devices for measuring in a continuous manner the temperature of a heated injection nozzle; in order to be able to monitor the temperature close to the gate of such a nozzle, it is important for the thermocouple itself to be positioned as close as possible to the front portion of the nozzle. Very crucial and decisive is also the capability for the position of the thermocouple to be exactly determined and firmly stabilized. As a result, the probe, i.e, the detecting head of the sensor device, must be mounted in a very accurate and secure manner, in particular during the installation and the maintenance of the nozzle in the injection mould.
This requirement must be peremptorily complied with each time that the nozzle is removed for any reason, and the need therefore appears quite clearly for technical solutions to be available, which would enable the thermocouple to be quickly removed and re-assembled while anyway ensuring a most accurate and constant positioning thereof.
Known from the disclosure in the U.S. Pat. No. 5,405,258 is the practice consisting in inserting the probe or measuring junction of a thermocouple in the injection nozzle used to inject a molten thermoplastic resin; such a probe, although it is capable of ensuring the temperature of the resin to be monitored in a most accurate manner, does however require the use of some supplementary devices; it furthermore is solely held in its position by the contrasting pressure existing between the nozzle itself and the frusto-conical portion of the platen containing the hot runners. This practically is the cause of a greater complexity in installing the thermocouple, as well as a quite likely instability in the positioning of the same thermocouple device.
According to the method described in the U.S. Pat. No. 5,028,227, the thermocouple is positioned in close vicinity of the nozzle by providing an appropriate inclined bore on the outside of the nozzle and most carefully and accurately inserting the thermocouple therein. However, since each time that the nozzles have to be replaced, the need arises for the thermocouple to be first removed and the reinstalled on the new nozzle, the necessary degree of accuracy implied in the process is the unavoidable cause of a much longer time required for the same process to be carried out, as well as a greater complexity thereof.
From the disclosure in the U.S. Pat. No. 4,875,848 the solution is known, which consists in using the frusto-conical end portion of the nozzle to provide a cross blind hole 138 therein, in which the thermocouple is then inserted and accommodated. However, in view of ensuring a due stability to the whole assembly, the nozzle itself, the heating element associated therewith and also the thermocouple must be secured to each other, preferably by brazing or soldering, and this of course implies, further to the complexity of such an additional process, also the unavoidable drawback that, when the nozzle must be replaced, the need also arises for the thermocouple to be either brazed again thereto or even replaced with a new one.
Known from the disclosure in the U.S. Pat. No. 5,795,599 is the practice consisting in applying the the, mocouple by drilling or, anyway, providing in the front portion of the nozzle a hole extending towards the rear portion thereof, inserting the thermocouple therein and bending the related lead wire backwards through a bend of half a round angle. Upon being so positioned on the nozzle, the thermocouple is stabilized, i.e. secured thereto through the application of an outer supplementary ring, which is provided with a plurality of appropriate appendices in a crown-like arrangement. After such a ring is duly applied so as to secure the thermocouple in its position, the appendices are bent by force so as to secure the ring, and therefore also the theruocouple, to the terminal portion of the nozzle. Such kind of solution can anyway be most readily appreciated to be characterized by its laboriousness during both the instailation and the removal of the thermocouple.
Known from the disclosure in the U.S. Pat. No. 5,326,251 is the practice consisting in arranging two distinct thermocouples in two respective positions in the final portion of the nozzle in view of more effectively controlling the course, i.e. pattern of the temperature gradient of the resin during the injection thereof into the mould. This actually proves particularly effective whenever plastic materials of different types and properties have to be processed. However, if this is not the case, the proposed solution appears to be unnecessarily complex.
Known from the disclosure in the U.S. Pat. No. 5,312,242 is, on the contrary, the practice consisting in providing a hollow tube acting as a sheath that surrounds and encloses the lead wire of the thermocouple for a certain length thereof. Such a sheath has actually the purpose of preventing possible resin leakages in the remaining parts of the mould from creeping along the thermocouple itself. This solution, however, does not involve any advantage as far as the techniques for installing and removing the thermocouple itself are concerned.
The U.S. Pat. No. 5,346,388 reveals a solution in which the thermocouple is accommodated in a manner that is similar to the one described in the afore mentioned U.S. Pat. No. 5,795,599, but is locked in position according to what is exemplified in the afore mentioned U.S. Pat. No. 5,405,258. It of course also repeats the drawbacks associated with the patents.